1. Field of the Invention
The present invention relates to a photosensitive polymer and to a chemically amplified photoresist composition containing the same, and more particularly, the present invention relates to a photosensitive polymer which includes a copolymer of alkyl vinyl ether and to a resist composition containing the same.
2. Description of the Related Art
As semiconductor devices become highly integrated, photolithography processes used in the manufacture of such devices must be capable of forming fine patterns. For example, sub-quarter micron or smaller sized patterns are needed for semiconductor memory devices having capacities exceeding 1 Gbit. Accordingly, conventional resist materials have limited applicability since they are utilized in conjunction with krypton flouride (KrF) excimer lasers having wavelengths (248 nm) which are too large for use in the formation of ultra-fine patterns. Thus, new resist materials have been proposed for use in conjunction with an argon flouride (ArF) excimer laser. This is because the ArF excimer laser has a wavelength (193 nm) which is smaller than that of the KrF excimer laser.
Present resist materials designed for use with ArF excimer lasers suffer several drawbacks as compared with conventional resist materials. The most common of these problems are low transmittance and poor resistance to dry etching. (Meth)acrylate polymers are generally used and widely known as ArF resist materials. The most typical of these resist materials is the poly(methyl methacrylate-tert-butyl methacrylate-methacrylic acid) terpolymer system manufactured by IBM, Inc. However, such polymers exhibit a weak resistance to dry etching.
To obtain an increased resistance to dry etching, a polymer having a backbone composed of an alicyclic compound such as an isobornyl group, an adamantyl group or a tricyclodecanyl group, is used. However, the resulting resist still exhibits an unacceptably weak resistance to dry etching since only a small portion thereof is occupied by alicylic groups.
Also, since the alicyclic compound is hydrophobic, in the case where the alicyclic compound is contained in the terpolymer, a degree of adhesiveness to underlying layers is deteriorated.
In an attempt to solve this problem, the following tetrapolymer has been proposed in which a carboxylic acid group is introduced to the backbone of the polymer (see J. Photopolym. Sci. Technol., 7(3), 507 (1994).): 
However, the resist layer obtained from the polymer having the above structure still exhibits a relatively poor adhesion to underlying layers, as well as a relatively poor resistance to dry etching. Also, the developing solution that is commonly employed during the development process must be diluted before being used.
Alternatively, a methacrylate copolymer having an alicyclic protecting group represented by the following formula has been proposed (see J. Photopolym. Sci. Technol., 9(3), 509 (1996).): 
An adamantyl group for increasing the resistance to dry etching and a lactone group for improving the adhesion characteristic have been introduced to the backbone of the methacrylate copolymer having the above structure. As a result, the resist layer obtained from the polymer having the this structure does exhibit an improved resolution and depth of focus, but the resistance to dry etching is still relatively poor. Also, severe line edge roughness is observed when a line pattern is formed from the resist layer.
Also, the manufacturing cost associated with raw materials used to prepare the copolymer is very high. In particular, the cost of a monomer having a lactone group introduced thereto (to improve an adhesion characteristics) is so prohibitive as to make it difficult to commercially use the monomer.
Another conventional polymer is a cycloolefin-maleic anhydride (COMA) alternating polymer represented by the following formula (see J. Photopolym. Sci. Technol., 12(4), 553 (1999) and U.S. Pat. No. 5,843,624.): 
While the fabrication cost associated with raw materials needed to prepare a copolymer such as the COMA system is low, the yield of the polymer is noticeably reduced. Also, the transmittance of the polymer at short wavelengths, for example, 193 nm, is very low. Further, since such polymers have an alicyclic group in their backbone which is strongly hydrophobic, they have poor adhesion characteristics.
Also, due to the structural characteristics of the backbone, these polymers have a high glass transition temperature of about 200xc2x0 C. or higher. As a result, it is difficult to carry out an annealing process to remove a free volume present in a resist layer obtained from such polymers. Thus, the resist layer is susceptible to an ambient environment. For example, the resist pattern may suffer a T-top profile. Also, in post-exposure delay (PED), the resist layer exhibits a decrease in stability to an ambient atmosphere, which entails many problems in a variety of processes using the resist layer.
It is an object of the present invention to provide a photosensitive polymer which has a high resistance to etching and improved adhesion to a substrate, while at the same time be capable of fabrication at a relatively low cost.
It is another object of the present invention to provide a resist composition which exhibits good lithographic characteristics during lithographic processes of both short wavelength radiation of 193 nm and deep UV radiation of 248 nm.
Accordingly, to achieve the above and other objects of the present invention, there is provided a photosensitive polymer comprising a copolymer of alkyl vinyl ether and maleic anhydride, represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are respectively represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is one of a hydrogen atom and a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group.
Preferably, R2 is methyl, ethyl, 2-hydroxy ethyl, n-butyl or iso-butyl group, and R3 is methoxy or ethoxy group.
The weight average molecular weight of the polymer is preferably in the range of 3,000 to 100,000.
According to another aspect of the present invention, there is provided a photosensitive terpolymer comprising:
(a) a copolymer of alkyl vinyl ether and maleic anhydride, represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are respectively represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is one of a hydrogen atom and a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group; and
(b) a comonomer having an acid-labile substituent or a polar functional group.
Preferably, the comonomer includes an acrylate derivative, a methacrylate derivative, a fumarate derivative, a styrene derivative or norbornene derivative.
The comonomer may have an alicyclic hydrocarbon group as the substituent.
Specifically, the comonomer is preferably an acrylate or methacrylate derivative and the photosensitive terpolymer is represented by the following formula and has a weight average molecular weight of the polymer in the range of 3,000 to 100,000:
wherein R4 is one of a hydrogen atom and a methyl group, R5 is an acid-labile C2 to C20 hydrocarbon group, and n/(m+n)=0.1 to 0.7.
Preferably, R5 is a t-butyl group or an acid-labile alicyclic hydrocarbon group. Examples of R5 include 2-methyl-2-norbornyl, 2-ethyl-2-norbornyl, 2-methyl-2-isobornyl, 2-ethyl-2-isobornyl, 8-methyl-8-tricyclo[5.2.1.02.6]decanyl, 8-ethyl-8-tricyclo[5.2.1.02.6]decanyl, 2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, 2-methyl-2-fenchyl or 2-ethyl-2-fenchyl group.
Particularly, the comonomer is preferably a norbornene derivative and the photosensitive terpolymer is represented by the following formula and has a weight average molecular weight of the polymer in the range of 3,000 to 100,000:
wherein R6 is one of a hydrogen atom and an acid-labile C2 to C20 hydrocarbon group, and n/(m+n)=0.1 to 0.7.
According to another aspect of the present invention, there is provided photosensitive polymer comprising:
(a) a copolymer of alkyl vinyl ether and maleic anhydride, represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are respectively represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is one of a hydrogen atom and a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group; and
(b) at least two comonomers consisting of acrylate, methacrylate or norbornene derivatives having an acid-labile substituent or a polar functional group.
According to still another aspect of the present invention, there is provided photosensitive polymer represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is one of a hydrogen atom and a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group; and
wherein R4 and R5 independently are one of a hydrogen atom and a C1 to C25 aliphatic hydrocarbon, R6 is one of a hydrogen atom and a methyl group, R7 is an acid-labile C2 to C20 hydrocarbon group, n/(m+n+o)=0.1 to 0.7, and o/(m+n+o)=0.1 to 0.7.
To achieve another object of the present invention, there is provided a resist composition comprising:
(a) a photosensitive polymer comprising a copolymer of alkyl vinyl ether and maleic anhydride, represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are respectively represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is one of a hydrogen atom and a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group; and
(b) a photoacid generator (PAG).
Preferably, the PAG is contained in an amount of 0.5 to 20% by weight based on the weight of the photosensitive polymer.
Examples of the PAG include triarylsulfonium salts, diaryliodonium salts, sulfonates or mixtures thereof, and others.
The resist composition according to the present invention may further include an organic base.
The organic base is preferably contained in an amount of 0.5 to 50 mol % based on the concentration of the PAG.
Preferably, the organic base is a compound comprising tertiary amine alone or in a mixture of at least two kinds thereof.
According to another aspect of the present invention, there is provided a resist composition comprising:
(a) a photosensitive polymer; and
(b) a photoacid generator (PAG), the photosensitive polymer comprising (a-1) a copolymer of alkyl vinyl ether and maleic anhydride and (a-2) a comonomer having an acid-labile substituent or a polar functional group, the copolymer being represented by the following structure: 
wherein X is one of a linear alkyl vinyl ether and a cyclic alkyl vinyl ether, which are respectively represented by the structures 
wherein y is one of the integer values 1 through 4, R1 is a hydrogen atom or a methyl group, R2 is a C1 to C20 hydrocarbon, and R3 is one of a hydrogen atom, a C1 to C3 alkyl group and an alkoxy group.
According to the present invention, a resist composition can be obtained which includes a copolymer of alkyl vinyl ether monomer and maleic anhydride, which entail very low fabrication costs, and which has excellent adhesion to underlying film materials and excellent resistance to dry etching. Also, since the photosensitive polymer according to the present invention has an appropriate glass transition temperature, an excellent lithographic performance can be achieved by employing the resist composition obtained therefrom in a photolithographic process.